1. Technical Field
The present invention relates to a wiring board for mounting a semiconductor element such as a semiconductor integrated circuit element.
2. Background
Conventionally, as a wiring board for mounting a semiconductor element such as a semiconductor integrated circuit element, a wiring board formed by a build-up method is known (for example, Japanese Unexamined Patent Application Publication No. 2006-210530). FIG. 3A is a schematic sectional view illustrating a state where a semiconductor element E′ is mounted on and a metal cap C′ is joined to a conventional wiring board 40 formed by the build-up method. FIG. 3B is a top view of the conventional wiring board 40. As shown in FIGS. 3A and 3B, the conventional wiring board 40 has a structure where an insulating layer 23 for the build-up and a conductor layer 24 for the build-up are laminated on the upper and lower surfaces of an insulating layer 21 for the core having a conductor layer 22 for the core. Furthermore, a solder resist layer 32 is deposited on a surface of the insulating layer 23 for the build-up and a surface of the conductor layer 24 for the build-up formed at the outermost layer. In this wiring board 40, the semiconductor element E′ is mounted on the upper surface and the metal cap C′ is joined to the upper surface so as to cover the semiconductor element E′. The lower surface of the wiring board 40 is a connection surface for connecting with an external electric circuit board. In FIG. 3B, a covered part by the solder resist layer 32 of the conductor layer 24 for the build-up formed at the outermost layer on the upper surface side is indicated by a broken line.
The insulating layer 21 for the core includes, for example, an electrically insulating material where a glass cloth is impregnated with a thermosetting resin such as an epoxy resin. In the insulating layer 21 for the core, a plurality of through-holes 25 penetrating from the upper surface to the lower surface of the insulating layer 21 for the core are formed. The conductor layer 22 for the core is deposited on the upper and lower surfaces of the insulating layer 21 for the core and in the through-hole 25. The conductor layer 22 for the core includes, for example, a highly conductive metal material such as copper foil or a copper plating layer. The inside of the through-hole 25 where the conductor layer 22 for the core is deposited is filled with a hole filling resin 26.
The insulating layer 23 for the build-up includes, for example, a thermosetting resin such as an epoxy resin. From the upper surface to the lower surface of the insulating layer 23 for the build-up, a plurality of via holes 27 are formed. The conductor layer 24 for the build-up is deposited on the surface of the insulating layer 23 for the build-up and in the via hole 27. The conductor layer 24 for the build-up includes a highly conductive metal material such as a copper plating layer.
A part of the conductor layer 24 for the build-up formed at the outermost layer on the upper surface side forms a circular semiconductor element connection pad 28 electrically connected to an electrode terminal of the semiconductor element E′. The semiconductor element connection pad 28 is formed in the row corresponding to an electrode terminal of the semiconductor element E′. The electrode of the semiconductor element E′ and the semiconductor element connection pad 28 are connected with a solder S1′ interposed therebetween.
Furthermore, another part of the conductor layer 24 for the build-up formed at the outermost layer on the upper surface side forms a frame-shaped cap connection pattern 29 connected to the metal cap C′. The cap connection pattern 29 is formed so as to surround the region where the semiconductor element connection pads 28 are formed. The metal cap C′ and the cap connection pattern 29 are joined with a solder S2′ interposed therebetween. The cap connection pattern 29 is connected to a ground potential. Therefore, the metal cap C′ connected to this cap connection pattern 29 with the solder S2′ interposed therebetween is also connected to the ground potential. As a result, the metal cap C′ functions as a shield against the semiconductor element E′.
A part of the conductor layer 24 for the build-up formed at the outermost layer on the lower surface side forms a circular external connection pad 30 electrically connected to the wiring conductor of the external electric circuit board. The external connection pad 30 is formed, for example, in a lattice shape.
The conductor layer 24 for the build-up includes wiring conductors for grounding, a power supply, and a signal. The wiring conductor for the grounding is electrically connected to the cap connection pattern 29. The wiring conductor for the signal includes a strip-shaped pattern 31 extending from the bottom of the semiconductor element connection pad 28 to the outside of the cap connection pattern 29 between the insulating layers 23 for the build-up formed on the upper surface side.
Furthermore, the solder resist layer 32 is deposited on the surfaces of the insulating layer 23 for the build-up and the conductor layer 24 for the build-up formed at the outermost layer on the upper surface side and lower surface side. The solder resist layer 32 includes a thermosetting resin such as an epoxy resin. In the solder resist layer 32, opening portions configured to expose the semiconductor element connection pad 28, the cap connection pattern 29, and the external connection pad 30 are formed.
However, in the conventional wiring board 40, the cap connection pattern 29 has a frame shape. Therefore, when the strip-shaped pattern 31 for the signal is attempted to extend to the outside of the cap connection pattern 29, it is necessary to extend the strip-shaped pattern 31 for the signal under the cap connection pattern 29 with at least one insulating layer 23 for the build-up interposed therebetween. Therefore, in the conventional wiring board 40, there has been a problem that the number of layers of the required insulating layers 23 for the build-up is increased, and that the thickness of the wiring board 40 is increased by the corresponding amount.